A load carried in a backpack is transmitted to the back and hips of a person wearing the pack through straps that pass from the top of the backpack, around the shoulders of the wearer, reattaching near the bottom of the backpack, as well as load transmission from the pack itself directly onto the back and hips of the wearer. Packs may also include a hip belt that secures the lower end of the pack to the user's hips for stability and additional load transference. To minimize a potential uncomfortable distribution of load on the user's shoulders, backpack shoulder straps are typically well padded. Conventional straps of recreational backpacks, such as those used for overnight hiking, are constructed from a nylon web, on the underside of which is secured an elastomeric foam pad. Similar pads may be incorporated into a hip belt.
Conventional methods of constructing the elastomeric foam pads incorporated into shoulder straps involve wrapping an elongate foam strip, that is cut from a sheet, with an outer fabric sleeve. In one type of construction, the foam pad is covered on a first side by a first sheet of fabric, and on an opposing side by a second sheet of fabric. The width of the fabric is equal to or slightly greater than the width of the foam pad. A length of nylon webbing is then folded over these edges of the fabric and/or foam pad, and a seam is stitched through the overlapped webbing, foam and fabric edges. This webbing secures the pad together, but may provide some discomfort to the user due to friction or pressure points along ridges presented by the band of webbing. Additionally, the folded and stitched edge construction may interfere with the transport of moisture from the wearer, trapping perspiration and causing additional discomfort.
In some conventional shoulder pads, the foam pad is contoured to taper in thickness along the edges. This tapered contour is created by compressing the pad to the desired contour while applying heat to the foam. This heat fuses the compressed material, leaving a permanent contour after the pad has cooled. This contouring creates a smoother edge termination, to reduce the thickness and resulting pressure points along the edge webbing. However, these compressed regions also have a much greater density than the remainder of the foam, making the pad less flexible along these lines, again potentially leading to discomfort. The compressed regions of the foam also lose a substantial portion of their breathability due to the loss of air cells.
Alternate backpack constructions involve pulling a pad through a sewn tubular fabric sleeve. This eliminates the need for edge webbing. However, the pad may shift or bunch undesirably within the surrounding sleeve. Additionally, there is a seam allowance, consisting of the sewn and folded edges of the fabric, that provides an undesirable pressure ridge along the foam due to the increased thickness of the fabric of the seam allowance. To prevent shifting of the foam within the sleeve, stitching may be made longitudinally or periodically along the length of the shoulder pad. While eliminating shifting of the pad within the sleeve, this introduces additional areas of compressed and stiff foam.
There thus exists a need for backpack shoulder strap pads, and similarly constructed hip belt pads, that incorporate fabric coverings on foam pads in a manner that does not alter the density of the foam pad or create external ridges.